Should we commune with other Christians with different beliefs than ours?

Thanks for your question. Let’s answer this question in several different units of thought.

Feeding the Hungry

Feeding the hungry is biblical (Isa. 58:10; Psa. 146:7; Matt. 25:35-37; Jas. 2:15-16, etc.). This is one of the works that the true believer is saved “unto”, but not “by”. Feeding the hungry is the work of the Spirit through believers and glorifies God.

A Definition of the True Church

In the language of the WCF the “invisible” church makes up the “whole number of the elect, that have been, are, or shall be, gathered into one, under Christ the Head thereof” (WCF 25.1). On the other hand the “visible” church is the body of the faithful (1 Cor. 12:27; Eph. 2:21–22) consisting of those throughout the entire world who outwardly profess faith in Christ, together with their children (WCF 25.2).

Though some churches may have some doctrinal errors and therefore somewhat obscure the Gospel, some have not so blotted out the truth of the Gospel so that no part of it remains in their preaching and how they ultimately live in Christ. We should understand that no one individual, church, or denomination is perfect before Holy God, including any church we ourselves may attend.

Unity of Believers

Anyone reading the Bible knows of many first century problems between both believing Jews and the Gentiles (Acts 15:1-2; Gal. 2:11-14, etc.). There were disagreements over food (Rom. 14:2-4) and days of the week (Rom. 14:5-9), etc. There was serious debate as to whether both groups were of the same faith. However, though they varied somewhat in some of their understanding of the truth, they discovered and in finality taught that they belonged together in the one faith of Jesus Christ (Acts 15:6-9; Eph. 3:1-6, etc.). They were one in Christ Jesus (Gal. 3:28).

Romans 15:4-7 calls us to unity with other Christians that may not fully agree with our all our beliefs (cf. Rom. 15:2). Paul writes,

4 For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope. 5 May the God of endurance and encouragement grant you to live in such harmony with one another, in accord with Christ Jesus, 6 that together you may with one voice glorify the God and Father of our Lord Jesus Christ. 7 Therefore welcome one another as Christ has welcomed you, for the glory of God.

Let’s unpack some of this pericope (i.e. group of verses). Notice that the things written before Paul wrote the book of Romans were written for our “instruction” (Rom. 15:4). This refers primarily to the Old Testament. This instruction was given primarily to the Jews first (cf. Rom. 9:4-5), but since the Cross Gentiles are now included as well (note they were included in the O.T. as well [i.e. Jethro, Ruth, Rahab, Naaman, Darius, Nebuchadnezzar, Jonah], but not as emphasized as the nation of Israel was). Look at the reason for this instruction; so that in good and bad times Christians would “endure” and be “encouraged”, so that we would continue to have “hope”.

Notice Paul’s hope/prayer in Romans 15:5; that God in all his grace would give to all in Christ endurance and encouragement to ‘live in harmony with one another, in accord with Christ Jesus’, so that all of us ‘together may with one voice glorify the God and Father of our Lord Jesus Christ’ (Rom. 15:6). Notice the words “harmony”, “accord”, and “together”.

So, in response to the hope laid out above we should “welcome one another” so that we may more fully glorify God together as one in Christ Jesus (Rom. 15:7).

In Essentials Unity, In Non-Essentials Liberty, In All Things Charity

Those who are united by faith in Christ are united to one another in the “body of Christ”, called the church (Eph. 5:23; Col. 1:24; cf. Rom. 12:5; 1 Cor. 10:17; Eph. 4:12; Heb. 13:3). We call this union the communion of saints. The Apostle’s Creed also speaks of believing in the “communion of saints.” It’s biblical and part of a faithful church’s confession.

The diverse range of theological beliefs and practices among Christians is well known in the pages of the New Testament (Rom. 14:2, 5, etc.). Even today Christian denominations don’t always agree on every issue. How do we deal with such differences among us? Paul states, “As for the one who is weak in faith, welcome him, but not to quarrel over opinions” (Rom. 14:1). Notice the phrase “welcome them” just as in Romans 15:7 (“welcome one another”). So, someone we may consider weaker in their beliefs are to be welcomed, in genuine love, so they may continue in the faith and so that both the weak and strong may continue to grow together (“iron sharpens iron”, Prov. 27:17). This is “the more excellent way” (1 Cor. 12:31; cf. Col. 3:14).

I personally believe that Christ won’t be coming back for his invisible church until this unity is being more fully lived out today (cf. Psa. 133:1-3; John 17:20-26). In the beginning pages of the book of Revelation, the Spirit instructs the seven churches (i.e. the universal church) to all get in step with the one Gospel delivered to the saints (cf. Jude 1:3). Of course full unity will be in the last day. And in heaven we observe, “a great multitude that no one could number, from every nation, from all tribes and peoples and languages, standing before the throne and before the Lamb, clothed in white robes, with palm branches in their hands (Rev. 7:9-10). Notice above the diverse groups in perfect unity being expressed! Since this is the genuine Christian’s future, then it only makes sense that we should be obedient to the scripture today and glorify God together in one accord.

An Answer to Your Question

You wrote of a “liberal Baptist Church.” I’m not sure exactly what this means. However, in general terms Baptist Churches affirm the death, burial, resurrection, and ascension of Jesus Christ. They affirm the virgin Birth. They indeed believe Jesus is God and in salvation by grace through faith, etc. They affirm the Apostle’s Creed. So, they are part of the visible church, as much as a faithful Presbyterian church down the street.

I believe in most cases gathering together with other Christians to feed the hungry or any other good work is what Christ desires/demands us to do. Of course I’m speaking of churches that sincerely confess the Apostle’s Creed and not cults, LGBT churches, etc. I hope this answer helps.